1. Field of the Invention
The present invention pertains to azeotropic and azeotrope-like compositions of 1,1,3,3-pentafluoropropane (HFC-245fa) and hydrogen fluoride.
2. Description of the Prior Art
In recent years there has been universal concern that completely halogenated chlorofluorocarbons (CFC's) might be detrimental to the Earth's ozone layer. Consequently, there is a worldwide effort to use fluorine-substituted hydrocarbons which contain fewer or no chlorine substituents. In this regard, 1,1,1,3,3-pentafluoropropane, a hydrofluorocarbon (HFC) having zero ozone depletion potential, is being considered as a replacement for chlorofluorocarbons such as dichlorodifluoromethane in refrigeration systems and trichlorofluoromethane as a blowing agent. The production of HFC's, i.e. compounds containing only carbon, hydrogen and fluorine has been the subject of interest to provide environmentally desirable products for use as solvents, blowing agents, refrigerants, cleaning agents, aerosol propellants, heat transfer media, dielectrics, fire extinguishing compositions and power cycle working fluids. It is known in the art to produce fluorocarbons such as HFC's by reacting hydrogen fluoride with various hydrochlorocarbon compounds. Such HFC's are not only considered to be much more environmentally advantageous than hydrochlorofluorocarbons (HCFC's) or chlorofluorocarbons (CFC's) because they are not non-ozone depleting, but also they are also non-flammable, and non-toxic as compared to the chlorine containing compounds.
HFC-245fa is well known in the art as described in U.S. Pat. No. 2,942,036, Canadian 684,687, EP 381 986A, JP 02,272,086 and WO 95/04022. All of the foregoing patents are incorporated herein by reference.
It has now been found that an important intermediate in the production of substantially pure 1,1,1,3,3-pentafluoropropane, is an azeotrope or azeotrope-like mixture of 1,1,1,3,3-pentafluoropropane and hydrogen fluoride. This intermediate, once formed, may thereafter be separated into its component parts by extraction techniques, even though they have close boiling points. HFC-245fa has a boiling point of about 14.degree. C. and HF has a normal boiling point of about 20.degree. C. at standard atmospheric pressure, which makes it particularly useful as a blowing agent or aerosol propellant. The azeotropic and azeotrope-like compositions find use not only as intermediates in the production of HFC-245fa, but they are additionally useful as solvents, as well as compositions for removing surface oxidation from metals. In addition, the formation of an azeotropic or azeotrope-like composition of 1,1,1,3,3-pentafluoropropane and hydrogen fluoride is useful in separating a mixture of 1,1,1,3,3-pentafluoropropane and an impurity such as 1,1,1-trichloro4,4-dichlorobutane (HCC-240fa). When it is desired to separate a mixture of 1,1,1,3,3-pentafluoropropane and an impurity, HF is added to form an azeotropic mixture of 1,1,1,3,3-pentafluoropropane and hydrogen fluoride, and then the impurity is removed from the azeotropic mixture, such as by distillation, scrubbing or other known means.